Treatment of tumors can be difficult in cancer patients due to the location of the tumors. They are often in locations that are difficult or impossible to reach through conventional surgery. If surgery is possible, it can be difficult to ensure that all portions of the tumor are removed. Remnants of a tumor left in a patient after surgery can result in regrowth of the tumor over time. Instead of surgery, it may be possible to kill tumor cells by heating them. For example, small iron particles can be injected into a tumor and heated using an alternating magnetic field, which can result in tumor cell damage or death.